1. Field of the Invention.
this invention relates to a method and apparatus for removing microparticulates from gas and more particularly to such a method and apparatus which employs rotating screens for comminuting such particles and changing their electrostatic charges in conjunction with spiral vortex zones followed by exposure to centrifugal fans through which the remaining microparticulates are effectively eliminated from the gas.
2. Description of the Related Art.
In advanced electrical power generation systems, fuel gases are generated from raw fuel, these gases being cleaned as best can be done and then combusted to yield expanded combustion gases that are employed to drive a gas turbine. The fuel and combustion gases are generally cleaned from microparticulates by means of high efficiency cyclones which are capable of removing up to 98% of such particles. The remaining 2% of the particles are very difficult to remove due to their small size, electrostatic charges and flocculating tendencies. These residual microparticulates which are generally composed of ash or char can seriously damage the turbine blades resulting in inefficiency of operation and downtime for repair as well as the expense of such repair. It is therefore highly desirable to effectively remove such residual microparticulates.
In the September, 1995 edition of Power Engineering magazine in an article on Coal Combustion(pages 15 and 20, a pressurized fluidized bed combustor is described which employs crushed coal and sorbent for generating gases for driving a gas turbine. Particles are removed from the gas in this system by means of a series of cyclones which removes about 98% of the particulate material. An attempt is made in this system to remove the remaining 2% of the particulate material by passing the gas through ceramic candles(ceramic candle batteries). While the ceramic candles are useful in removing some of the particulate material they have cleaning problems and often break down and fail. This approach also has the disadvantage of requiring high temperature, high pressure filters which generally have limited operating lives.
In my application Ser. No. 08/423,326 of which the present application is a continuation in part, a grinding system is described in which rotating screens with wide mesh openings are first used to comminute the material through spiral vortexes and such comminuted material is then fed to circular vortexes formed between rotating discs and stationary plates where the final grinding of the particulate material is accomplished and the final comminuted material is separated from the gas streams by centrifugal fans. The system and method of the present invention applies some of the technology of my prior art patent application in implementing the separation of the microparticulate material from the fuel gas.